In order to improve the surface of plastic lenses which became used widely in recent years, as a component for a hard coating agent to be applied to said surface, sols of a metal oxide having a high refractive index have been used.
A stable sol of tungstic oxide alone has not been known yet, but a sol having a WO3:SiO2:M2O molar ratio (wherein M is an alkali metal atom or an ammonium group) of 4 to 15:2 to 5:1, obtained by addition of a silicate, has been proposed (e.g. JP-A-54-52686).
A silicate-stannate composite sol having a molar ratio of Si:Sn of 2 to 1000:1, has been proposed (e.g. JP-B-50-40119).
A hard coating agent which contains particles of an oxide of a metal such as Al, Ti, Zr, Sn or Sb, having particle sizes of from 1 to 300 nm, has been disclosed (e.g. JP-B-63-37142).
A stable sol containing colloidal particles of a modified metal oxide having particle sizes of from 4.5 to 60 nm, which comprise colloidal particles of an oxide of a metal with a valence of 3, 4 or 5, having particle sizes of from 4 to 50 nm, as nuclei, and colloidal particles of a tungstic oxide-stannic oxide composite having a WO3/SnO2 weight ratio of from 0.5 to 100 and having particle sizes of from 2 to 7 nm, covering the surface of the colloidal particles as nuclei, wherein the content of the total metal oxides is from 2 to 50 wt %, has been proposed (e.g. JP-A-3-217230).
A stable sol of a modified SnO2—ZrO2 composite which contains particles comprising colloidal particles of a SnO2—ZrO2 composite having a weight ratio of ZrO2/SnO2 of from 0.02 to 1.0 and having particle sizes of from 4 to 50 nm, as nuclei, and colloidal particles of a WO3—SnO2 composite having a WO3/SnO2 weight ratio of from 0.5 to 100 and having particle sizes of from 2 to 7 nm, covering the surface of the colloidal particles as nuclei, has been proposed (e.g. JP-A-6-24746).
A stable modified metal oxide sol containing particles (C) which comprise, as nuclei, colloidal particles (A) of a metal oxide having primary particle sizes of from 2 to 60 nm, and a coating (B) comprising colloidal particles of an acidic oxide, covering the surface of the nuclei, wherein the particles (C) are contained in a proportion of from 2 to 50 wt % as calculated as metal oxides, and having primary particle sizes of from 2 to 100 nm, has been disclosed. Further, a sol wherein the metal oxide particles as the nuclei are SnO2 particles or SnO2—ZrO2 composite colloidal particles, and the coating is made of alkylamine-containing Sb2O5 particles (M/Sb2O5 molar ratio of from 0.02 to 4.00) has been disclosed (e.g. JP-A-2001-122621).
A process for producing a silicate-antimonate composite sol liquid or a silicate-stannate composite sol liquid, which comprises mixing an alkali silicate aqueous solution or a silicate sol liquid with an alkali antimonate aqueous solution or an alkali stannate aqueous solution in a molar ratio of Si:Sb or Si:Sn of 2 to 1,000:1, and subjecting the mixed liquid to cation exchange with an acid form ion exchanger, has been disclosed (e.g. JP-B-50-40119).
A silica-antimony oxide composite sol having antimony oxide colloidal particles containing an inorganic silicate compound in an amount of from 0.1 to 50 wt % as SiO2 dispersed in a dispersion medium, has been disclosed (e.g. JP-B-7-25549).
Plastic molded products are used in a large quantity by virtue of their advantageous features such as light weight, good processability and high impact resistance. On the other hand, they have drawbacks that the hardness is inadequate, and thus they are susceptible to scratching, they are likely to be eroded by a solvent, they are likely to be electrified and adsorb a dust, and the heat resistance is inadequate. Thus, as compared with inorganic glass molded products, they were practically inferior for use as lenses for eyeglasses or window materials. Accordingly, it has been proposed to apply a protective coating to a plastic molded product. Many compositions have been proposed as coating compositions to be used for such a protective coating.
“A coating composition containing an organic silicon compound or its hydrolysate as the main component (resin component or coating film-forming component)” which was expected to provide a coating film as hard as an inorganic product, has bee used for eyeglass lenses, (e.g. JP-A-52-11261).
This coating composition still does not provide adequate scratch resistance. Accordingly, one having colloidal silica particles added to the above coating composition has been proposed, which is used practically for eyeglass lenses (e.g. JP-A-53-111336).
Heretofore, plastic lenses for eyeglasses have been produced by casting diethylene glycol bisallyl carbonate in a monomer state, followed by polymerization. The lenses produced in such a manner have a refractive index of about 1.50, which is low as compared with the refractive index of about 1.52 of glass lenses, and in the case of lenses for short sighted, there is a problem that the peripheral thickness has to be increased. Accordingly, in recent years, there has been development of monomers having higher refractive indices than the diethylene glycol bisallyl carbonate, and resin materials having high refractive indices have been proposed (e.g. JP-A-55-13747, JP-A-56-166214, JP-A-57-23611, JP-A-57-54901, JP-A-59-133211, JP-A-60-199016 and JP-A-64-54021).
For lenses made of such resins having high refractive indices, a method of using a colloidal dispersion of fine particles of an oxide of a metal such as Sb or Ti, for a coating material, has been proposed (e.g. JP-A-62-151801, JP-A-63-275682).
Further, a coating composition comprising a silane coupling agent, and a stable modified metal oxide sol containing particles (C) which comprises, as nuclei, colloidal particles (A) of a metal oxide having primary particle sizes of from 2 to 60 nm, and a coating (B) comprising colloidal particles of an acidic oxide, covering the surface of the nuclei, wherein the particles (C) are contained in a proportion of from 2 to 50 wt % as calculated as metal oxides, and having primary particle sizes of from 2 to 100 nm, has been disclosed. Further, a coating composition wherein the metal oxide colloidal particles as nuclei are SnO2 particles or SnO2—ZrO2 composite colloidal particles, and the coating is made of alkylamine-containing Sb2O5 particles (M/Sb2O5 molar ratio of from 0.02 to 4.00) has been disclosed (e.g. JP-A-2001-123115).